(1) Field of the Invention
The present invention relates to liquid crystal display panels in which a thin film transistor is used as an active element, and more particularly to a display panel which ensures the enhancement of aperture efficiency and pixel driving capability by efficient design and arrangement of the structural element of the display panel, e.g. data lines, gate lines, thin film transistors, and pixels.
(2) Description of the Related Art
In the field of image processing for information transmission, many image display devices have been developed. In particular, various flat panel display devices have taken the place of conventional cathode ray tubes.
Techniques for making liquid crystal displays which are small in size, light in weight, and have low voltage driving performance and low electric power-consumption have improved. In particular, active matrix type liquid crystal display devices have been made by blending manufacturing techniques for liquid crystal displays and semiconductor devices. Such a method enhances display quality by providing non-linear switching devices to each pixel arranged in a matrix. These switching devices may be made of thin film transistors of amorphous silicon.
In order to improve the quality of liquid crystal display panels, data lines, gate lines, switching devices and electrodes should be designed such that improvements in switching devices, aperture efficiency and processing space are possible.
There has been proposed a panel in which thin film transistors are formed directly on gate lines in order to increase the aperture efficiency, that is, to maximize the size in pixels of the aperture for allowing light to pass. This conventional delta shape display panel is shown in FIG. 5 and has been manufactured by SHARP Electronics Corporation.
As shown in FIG. 5, gate lines 53.sub.n (n=1, 2, . . . , n) and data lines 52.sub.n (n=1, 2 . . . , n) are arranged in a matrix, and thin film transistors are disposed directly on the gate lines 53.sub.n adjacent to each intersection of the gate lines and data lines. The gate lines serve as gate electrodes. Drain electrodes 55 are connected to liquid crystal cells through source electrodes 54 and pixel electrodes 57.
Data lines 52.sub.n are formed to be level with and perpendicular to gate lines 53.sub.n so that electrodes of thin film transistors may be suitably formed on gate lines 53.sub.n, i.e., so that device formation regions and pixel electrodes 57 are secured.
Source electrodes 54 are formed integrally with data lines 52.sub.n, and drain electrodes 55 are spaced from source electrodes 54. Semiconductor layers 56 and insulating layers (not shown) are formed between the device formation regions of gate lines 53.sub.n, and source and drain electrodes 54 and 55.
Such a display panel increases the area of the pixel electrodes 57 by disposing the device formation regions directly on gate lines 53.sub.n. However, optimum aperture efficiency is not ensured because regions of data lines 52.sub.n including the source electrodes 54, encroach on the regions of the pixel electrodes 57.
The source and drain electrodes 54 and 55 are wired on the device formation regions, and signals may be transmitted from a source electrode 54 to a drain electrode 55 via channel layers 56, which are semiconductor layers. The width of channel layers 56 is limited by the source and drain electrodes 54, 55 and depends on the shape of the electrode pattern.
The channel width can be improved so as to satisfactorily supply on-currents to pixel electrodes requiring a larger driving current. However, the increase in the width of the gate electrodes is closely related to the width of the gate lines 53.sub.n. Also, increased gate electrode width is not desirable in view of the size of the display device, and because off-currents are increased at the same time.
Also, since the devices arranged in a matrix are formed directly on the strip-shaped gate lines 53.sub.n, the gate lines 53.sub.n require a large width so that the channel width, source and drain electrodes 54, 55 may be formed without misalignment.